In addition to the major endogenous estrogens, specific estrogen metabolites (including 16alpha(OH) estrone, 4-(OH) estrone, and 4-(OH) estradiol) are thought to be genotoxic and potentially carcinogenic in humans. One mechanism by which these estrogen metabolites are thought to exert their carcinogenic effects is the formation of electrophilic quinone products that react with DNA to form depurinating adducts known to generate mutations that initiate cancer in both in vitro and in vivo studies. Despite the potential importance of endogenous estrogen metabolites and DNA adduct formation in breast carcinogenesis, no studies have investigated their association with human breast cancer risk. This lack of data is due in part to the lack of a method of analysis for estrogen-DNA adducts in human biological fluids. Development of an inexpensive, rapid method will enable the performance of epidemiologic studies that determine the associations between specific estrogen DNA adducts and breast cancer risk, as well as the associations between these compounds and modifiable risk factors such as obesity and diet. The main purpose of this project is to develop a rapid, specific, and sensitive method of analysis of endogenous estrogen metabolite-DNA adducts, that will be practical for use in large epidemiological studies. The specific aims of this project are to develop and validate an HPLC-ESI-MS/MS method for analysis of urinary estrogen DNA adducts, such as 4(OH)-E1 (E2)-1 (alpha,beta)-N7Guanine. Urine from the midfollicular and midluteal phases of the menstrual cycle, as well as from postmenopausal women, will be analyzed for determination of quality control parameters. The development of this method will enable the performance of large epidemiological studies of estrogen metabolism, DNA adducts, and breast cancer, that will contribute to our understanding of the mechanisms by which estrogen influences breast cancer risk.